Posted
by
Soulskill
on Sunday May 30, 2010 @11:48AM
from the but-blanche-and-dorothy-didn't-believe-her dept.

astroengine writes "The flying telescope SOFIA took its maiden flight on Wednesday, and its 'first light' images have already been released. The cool thing about SOFIA is that it flies high enough (integrated inside a converted 747, taking it to an altitude of 41,000 ft) to carry it above 99% of the atmosphere's infrared-absorbing water vapor. This means it can collect 80% of the IR radiation that hits orbital telescopes (like NASA's Spitzer) but without the huge cost of being launched into space. Also, SOFIA is expected to last 20 years, many times the operational lifespan of space missions. Already, SOFIA has returned stunning results, including the observation of heat leaking through Jupiter's clouds, heat that was generated billions of years ago when the gas giant was forming."

I heard about this a while back [nasa.gov] and am still puzzled as to how you isolate a space telescope from vibrations while its still somewhat within the atmosphere. Is there very little or no turbulence at its flight altitude?

IT never fails to amaze me that NASA does not send a balloon to 100,000 feet and load it up with all kinds of scientific equipment. That way, they would have advantages of being almost in space, but for a fraction of the cost of sending anything in space.

Also, infrared instruments usually need to be actively cooled, which means that the spacecraft needs a supply of coolant, such as liquid nitrogen. The coolant usually runs out long before anything on the spacecraft breaks down. So, the lifespans of space-based infrared telescopes tend to be limited by the amount of coolant that can be stored onboard. Sofia does not have that problem because it can refill its tanks every time it finished flying.

Indeed. But Hubble's optics and instruments are optimized for operating in the near-ultraviolet and visible ranges. The more recent Spitzer telescope operates in infra-red (3 micron to 180 micron), so it is a more salient comparison. Spitzer's operational life is limited by its coolant supply of 360 liters of liquid helium http://www.spitzer.caltech.edu/technology/cryostat.shtml [caltech.edu], unlike Hubble, which does not need cryogenics.

The telescope is mounted on a spherical bearing with gyroscopic stabilization and image feedback to correct for drift. This takes care of rotations. For translations, there is a damped spring mechanism holding the whole kaboodle to the support bulkhead (the image doesn't care if the telescope is translated, as it is "inifinitely" far away; however sudden translations can cause the telescope to flex, moving the image plane). And the pilots are very, very skilled at keeping constant and very precise attitudes. It's remarkably stable.

Um, they do and do so regularly.
http://www.csbf.nasa.gov/ [nasa.gov]
http://astrophysics.gsfc.nasa.gov/balloon/ [nasa.gov]
Balloons hoisting 2000kg+ payloads, up for weeks at a time, at elevations over 30-35km.
When working in the 90's at JPL in Southern California, I would occasionally have lunch with a guy responsible for launching huge skids of scientific equipment at Palastine, TX, at the National Balloon Facility. Palastine is convenient due to the large amount of helium produced as a waste product from the wells in the area.
Palastine's accomplishments notwithstanding, Southern California is also home to cutting-edge balloon experimenters.
http://en.wikipedia.org/wiki/Larry_Walters [wikipedia.org]

No, it's not. If you're in view of the sun it's incredibly hot. And even when it's cold there's no medium to absorb your waste heat. In the same way that water cools you faster than air because water is denser, a void won't cool you at all beyond what you can naturally radiate away.

It doesn't matter how cold it is if there's no medium to suck up your heat. Again, there's a reason 80F air feels warmer than 80F water: water is thicker and so transmits radiation (eg, heat) more efficiently. A void won't transmit any heat at all, unless you're pushing it out.